{"id":4044,"date":"2026-07-27T17:44:47","date_gmt":"2026-07-27T17:44:47","guid":{"rendered":"https:\/\/discussions.weather.arizona.edu\/?p=4044"},"modified":"2026-07-27T17:49:38","modified_gmt":"2026-07-27T17:49:38","slug":"thunderstorms-restricted-to-mogollon-rim-and-international-border-today-july-27th-2026","status":"publish","type":"post","link":"https:\/\/discussions.weather.arizona.edu\/?p=4044","title":{"rendered":"Thunderstorms restricted to Mogollon Rim and International border today: July 27th, 2026"},"content":{"rendered":"\n

Summary<\/h2>\n\n\n\n

Upper-level water vapor shows that two hurricanes, Fausto and Genevieve, are present in the Pacific; Genevieve is expected to move away from Mexico, while Fausto will weaken as it passes north of Hawaii. A polar low over Baja California has absorbed a Tropical Upper Tropospheric Trough (TUTT); it is forecast to move up the California coast around the subtropical high. Across Arizona and New Mexico, dry air aloft has mixed down and suppressed dewpoint temperatures, and forecast soundings indicate little potential for valley storms today due to not reaching convective temperatures and warming at 500mb.<\/p>\n\n\n\n

Thunderstorm activity will be limited mainly to mountains and the International border, with westward movement into Mexico and outflow-driven storms in southern Arizona. Tomorrow, slightly stronger winds may help push storms westward, but significant precipitation is not expected for the valleys. <\/p>\n\n\n\n

The overall outlook remains a low-grade monsoon pattern, with storm chances further decreasing as warm air aloft persists through to the end of July. A westward shift in the subtropical high-pressure could eventually bring more favorable monsoon flow conditions in August.<\/p>\n\n\n\n

Yesterday’s Weather<\/h2>\n\n\n\n

Yesterday\u2019s visible satellite imagery shows thunderstorms were isolated over the southern half of Arizona and New Mexico as strong winds at the cirrus level sheared the tops of the thunderstorms off, as shown from where the storm was (green marker) to where the leading edge of the cirrus was (the blue marker). The cirrus was riding westward on 50-knot winds. To get winds aloft this strong requires convergence resulting in sinking air (subsidence). The areas of clear sky in southern Arizona\u00a0are\u00a0where the subsidence was strongest. Thunderstorms from the Mogollon Rim and north were not affected by the subsidence, but this was a down day compared to the activity on Saturday.\u00a0<\/p>\n\n\n

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GOES-19 visible satellite imagery overlaid with GLM lightning flashes from July 26th from 4 pm, College of DuPage.<\/figcaption><\/figure>\n<\/div>\n\n\n

There was no reported rainfall reported on either the Pima or Maricopa Flood Control alert gauges. The Rainlog\u00a0gauge observations show that thunderstorms were mostly in the mountains of Arizona and New Mexico.\u00a0<\/p>\n\n\n

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Rainlog.org 24-hour accumulated precipitation gauge observations<\/figcaption><\/figure>\n<\/div>\n\n\n

The HRRR-UA WRF 12Z 24-hour accumulated precipitation forecast (left) and corresponding observed precipitation from MRMS (right) are shown below.\u00a0Except for the overestimated forecast precipitation in Cochise and Santa Cruz counties, the rest of the region was well forecast.\u00a0<\/p>\n\n\n

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HRRR-UA WRF 12Z 24-hour accumulated precipitation forecast (left) and corresponding observed precipitation from MRMS (right) for July 26th.<\/figcaption><\/figure>\n<\/div>\n\n\n

The HRRR-UA WRF 15Z forecast was more accurate for precipitation in southeast Arizona. <\/p>\n\n\n

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HRRR-UA WRF 15Z 21-hour accumulated precipitation forecast for July 26th.<\/figcaption><\/figure>\n<\/div>\n\n\n

Analysis<\/h2>\n\n\n\n

A larger view from the GOES-19 satellite of upper-level water vapor shows two hurricanes (Fausto and Genevieve), two Tropical Upper Tropospheric Troughs (TUTT), and a polar low. A TUTT present yesterday\u00a0was absorbed by the polar low. Fausto will weaken as it moves north of the Hawaiian Islands; Genevieve will move west away from Mexico. The low in northern Mexico will move around the ridge up the California coast.\u00a0<\/p>\n\n\n

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GOES-19 upper-level water vapor image from July 27th at 7 am, College of DuPage.<\/figcaption><\/figure>\n<\/div>\n\n\n

The 60\u00b0F dew point temperature line has retreated south due to dry air aloft mixing down.<\/p>\n\n\n

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Surface weather station observations for Arizona and New Mexico at 7:00 am, NWS<\/a><\/figcaption><\/figure>\n<\/div>\n\n\n

The HRRR-UA WRF 12Z initialization (left) and observed (right) sounding for Phoenix at 5 am are alike, and the only difference is the higher\u00a0Convective\u00a0Available\u00a0Potential Energy (CAPE) on the observed\u00a0sounding because the surface dewpoint temperature is too high and not representative for the area (maybe nearby irrigation a factor here).<\/p>\n\n\n

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HRRR-UA WRF 12Z (left) initialization and observed sounding (right) at Phoenix for 5 am this morning.<\/figcaption><\/figure>\n<\/div>\n\n\n

At 250mb, the\u00a0monsoon ridge is in southeast Colorado while the polar jet stream is cutting across northern California.\u00a0A shortwave trough is across southwest Arizona extending south to the Baja Peninsula.\u00a0The trough resulted from the merger of\u00a0the\u00a0polar low-pressure system and a TUTT (discussed earlier).\u00a0Winds aloft are a little slower today and more from the southeast. Convergence is still noted in southeast Arizona.\u00a0<\/p>\n\n\n

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The shortwave trough at 300mb is not visible at the 500mb level; more upper-air data in Sonora would help here, e.g., Hermosillo.\u00a0The cooler\u00a0air marked in red may be a reflection of the trough at 300mb.\u00a0\u00a0<\/p>\n\n\n

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At 700mb, there\u2019s not much moisture except small amounts (65-70%) in Arizona with very weak circulation near Tucson.<\/p>\n\n\n

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Today<\/h2>\n\n\n\n

The\u00a0HRRR-UA WRF 12Z forecast\u00a0soundings\u00a0for Phoenix (left) and Tucson (right)\u00a0are amazingly similar at 4 pm. Both show precipitable water dropping during the day, and neither is\u00a0likely to\u00a0support storms in the valleys due to convective temperatures not being met. At 500mb in Tucson, there\u2019s warming of the vertical profile\u00a0too.\u00a0Although the wind speed aloft has dropped, there is still convergence at 300mb as noted in the analysis above. The convergence may lessen, especially south of Tucson, this afternoon and evening.<\/p>\n\n\n

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HRRR-UA WRF 12Z forecast soundings for Phoenix (left) and Tucson (right) at 4 pm.<\/figcaption><\/figure>\n<\/div>\n\n\n

Thunderstorms form in the afternoon in the mountains of northern Arizona, the Mogollon Rim, and western New Mexico. Other thunderstorms develop\u00a0along the International border south and east of Tucson. The thermal wind indicates they will be moving southwest and west toward higher CAPE values in Mexico. Some storms will develop along outflow boundaries\u00a0in southern Pima County this evening.<\/p>\n\n\n\n